THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE III, 2009, Vol.32, No.2, ISSN 1221-454X ELECTROTECHNICS, ELECTRONICS, AUTOMATIC CONTROL, INFORMATICS
SIMULATION RESULTS OF DOUBLE FORWARD CONVERTER
P. VIJAYA KUMAR1, Dr. S. RAMA REDDY2 1
Research Scholar, Jawaharlal Nehru Technological University, Hyderabad, India. 2 Professor, Jerusalem College of Engineering, Chennai, India. E-mail :
[email protected],
[email protected]
Abstract: This work aims to find a better forward converter for DC to DC conversion. Simulation of double forward converter in SMPS system is discussed in this paper. A forward converter with RCD snubber to synchronous rectifier and/or to current doubler is also discussed. The evolution of the forward converter is first reviewed in a tutorial fashion. Performance parameters are discussed including operating principle, voltage conversion ratio, efficiency, device stress, small-signal dynamics, noise and EMI. Its circuit operation and its performance characteristics of the forward converter with RCD snubber and double forward converter are described and the simulation results are presented Keywords: Forward converter with a RCD snubber, Forward converter with a LCDD snubber, Forward converter with a resonant switch, Forward converter with a switching snubber, Synchronous rectifier, Current doubler.
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1. INTRODUCTION
The forward converter remains as an industry workhorse in low-power DC/DC conversions. Recent development has significantly enhanced the performance and, in the mean time, increased the number of forward topologies that are available for a designer to choose from. Hence, selecting a best suitable forward topology for a given application becomes an important and challenging task. This paper presents a simulation of results of the forward converter. It is intended for design engineers who desire to be a successful in a first implementation of a design and to meet the increasingly demanding spec, budget, and schedule requirements. Topologies selected here are based on one criterion: whether or not a topology is used in industry applications. Personal preference also plays a role. Section 2 presents an account of the evolution of the forward converter. The account follows the
technology development of the forward. It starts with the classic forward and leads all the way to the contemporary topologies, including the forward/flyback converter and the double forward converter. For each topology, key design quantities are summarized together with respective strengths and weakness. Section 3 is a simulation results and compare the performance of the system and the basic topologies to include synchronous rectifier and the current doubler.
2. EVOLUTION OF THE FORWARD CONVERTER Discussion is focused on those forward topologies that are widely used in industry. It follows the line of technology development, using the reset mechanism as a common thread. Rather, it focuses on important design aspects such as reset mechanism, voltage conversion ratio, and device stresses.
This paper was recommended for publication by Emil Rosu 51
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE III, 2009, Vol.32, No.2, ISSN 1221-454X A. The Classic Forward Converter When M is turned off, a diode and a capacitor clamp the drain-source voltage in the same manner as in the case of a RCD snubber. Reset of the capacitor is accomplished through a LC resonance formed by Lr, Cr, and Dc1.The voltage stress on the MOSFET is typically 2.0Vin,max.By the nature of resonance, multiple modes of operation exist. Because of this, excessive design iterations are needed to ensure proper operation over all load, line, and transient conditions.
Circuit (a) in Figure 2 is the classic forward converter. The basic operation is well known (Severns and Bloom, 1985; Dong Tan, 1996; Severns, 2000; Bhat,and Dong Tan, 1989; Dong Tan, 2001). When the switch M is turned on, a positive voltage is applied to the primary of the transformer. By the action of the transformer a proportional voltage appears on the secondary. This voltage biases diode D1 into conduction, forwarding power to the output. A low pass filter, formed by Lf and Cf, recovers the DC voltage and attenuates switching ripple. Adjusting the duty ratio, defined as the on time over switching period, regulates output voltage.
Designers often find out that, while this technique controls the drain-source voltage well at turn-off, it offers elusive efficiency improvement. The reason is that the added conduction loss by the resonance can easily eat up the saving of the “lossless” snubber.
When M is turned off, an auxiliary winding resets the transformer through diode D. For the same number of turns, a common choice, the duty ratio is
